Weather Tidbits: The Pacific North American Pattern

We’ll be discussing the Pacific North American Pattern, also known as the PNA, in this edition of Weather Tidbits. The PNA is a sub-seasonal wavering jet stream climate pattern. This is in contrast to a seasonal, longer-lasting climate pattern like ENSO i.e. El Niño and La Niña. The PNA is influenced by the East Asian jet and the strength of air pressure in the Aleutian Islands. The PNA has both a positive phase and a negative phase. Each phase rarely persists for more than a week or two and has its own unique jet stream configuration with downstream effects on North American’s weather. During a negative PNA, a ridge of high pressure builds over the Aleutians with a downstream trough of lower pressure on the west coast, and a ridge resulting warmer weather over the east coast. A negative PNA has a building trough of lower pressure over the Aleutians, a ridge over the western U.S., and a trough over the eastern U.S.. This trough brings in cooler weather.